Tetrakis(hydroxymethyl)phosphonium sulphate(2:1)

Toxicity to microorganisms

Description of key information

OECD Guideline 209, GLP, key study, validity 1:
3h-EC50 = 18 mg/L (nominal, as main ingredient);
3h-NOEC = 2.4 mg/L (nominal, as main ingredient).

(For more details please read CSR available in section 13).

Key value for chemical safety assessment

EC50 for microorganisms:

18 mg/L

EC10 or NOEC for microorganisms:

2.4 mg/L

Additional information

Two studies are available to assess the inhibition of microbial activity by the active substance THPS. These studies were performed on the THPS in solution. The relevant results were expressed as main ingredient (100% active substance).

A respiration inhibition test (Mead, 1998) and a nitrification inhibition test (Mead, 2002) were performed. Both studies are of reliability 1. The study leading to the lowest EC50 value has been defined as key study (Mead, 1998).

The results of the available studies, expressed as main ingredient, are presented below:

Test method	Inoculum	Endpoint	Duration	Reliability	Flag	Results (EC50, mg/L)	Results (NOEC, mg/L)	Reference
OECD Guideline 209	Activated sludge of a predominantly domestic sewage	Respiration inhibition	3h	1	KS	18	2.4	Mead, 1998
ISO 9509	Activated sludge of a predominantly domestic sewage	Nitrification inhibition	4h	1	SS	42	2.0	Mead, 2002

In conclusion, the retained endpoints values for chemical safety assessment are:

- 3h-EC50 = 18 mg/L (nominal, main ingredient);

- 3h-NOEC = 2.4 mg/L (nominal, main ingredient).